Tool safety device for presses

ABSTRACT

A first limit switch on the press frame and a second on the bottom toolholding table are respectively actuated by a member on the main piston and by one on a sleeve that supports this table. The sleeve and piston together form a compressed air chamber that elastically supports the table above the piston during the earlier part of the working stroke. Excessively thick sheet metal or a foreign object on the sheet forces the table downwards against the air cushion to close the second limit switch prematurely with respect to the first, bringing the piston to an immediate stop.

O United States Patent 1111 3,568,553

[72] Inventors Walter Wanner; [56] References Cited Martin Maurer, Romanshorn, Switzerland UNITED STATES PATENTS if; 42%; 969 3,078,515 2/1963 Wintriss 100/53x [45] Patented Mar. 9, 1971 3,407,913 10/1968 Tezuka 83/58X [73] 'Assignee Hydrel A.G. Primary Examiner-William S. Lawson v R h S it l d Attorney-Singer, Stern and Carlberg [32] Priority May 2, 1968 3 3 1 Switzerland 6529/68 ABSTRACT: A first limit switch on the press frame and a [54] TOOL SAFETY DEVICE FOR PRESSE 3 Claims, 1 Drawing Fig.

s2 u.s.c1 t. 83758, 100/53 511 mac] B26d7/24 50 FieldofSearch 83/58; 100/53 second on the bottom toolholding table are respectively actuated by a member on the main piston and by one on a sleeve that supports this table. The sleeve and piston together form a compressed air chamber that elastically supports the table above the piston during the earlier part of the working stroke. Excessively thick sheet metal or a foreign object on the sheet forces the table downwards against the air cushion to close the second limit switch prematurely with respect to the first, bringing the piston to an immediate stop.

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Patented Mm 9,1971 3,568,553

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TOOL SAFETY DEVICE FOR PRESSES BACKGROUND OF THE INVENTION The invention relates to a safety device for protecting the tools of presses against damage.

When operating stamping presses it sometimes occurs that the cutting tools are damaged by excessively thick metal inadvertently placed in the press or by a foreign object, such as a piece of scrap, on the metal, the object, together with the metal, coming to be placed between the cutting tools of the toot set. I

SUMMARY OF THE INVENTION v BRIEF DESCRIPTION OF THE DRAWING The invention will be described in detail, with reference to the accompanying single FIGL, which is avery schematic longitudinal view in section of one embodiment of the invention, the two halves of the FIG. showing certain parts in different positions. 9

DESCRIPTION OF THE PREFERRED EMBODIMENTS The stamping press, having frame uprights 1 of which only a small part is schematically shown, comprises a vertically movable bottom toolholding table 2 and an oppositely positioned top toolholding table 3 that is fixed to the uprights l of the press frame. The two tables 2 and 3 respectively hold a bottom cutting tool 4, such as a blanking tool, and a complementary top cutting tool 5. The blank of sheet metal 6 that is to be blanked or punched is laid between these two tools, which are shown purely schematically as rectangles and are held in the customary way by the tables 2 and 3. To punch or blank the metal 6, the lower table 2 is raised in a manner to be explained. When only the metal 6 is located between the two complementary cutting tools 4 and 5, the press operates satisfactorily. But if some object 7, such as a piece of metal scrap, is on the sheet metal 6, it can, depending on its size and position and on the material of which it is made, cause not only a defective blanked or punched part but also considerable damage to the tools 4 and S. In accordance with the invention, the safety device that will now be described prevents further upward movement of the table 2 if some object 7 comes to be pressed against the upper tool 5.

The table 2 embodies two (or four) symmetrically positioned through holes 8, each holding a ball bearing or roller guide 9 for a sleeve 10. The sleeve has a head 12 movable up and down in a recess 11 of the table 2, and extends into a lower blind hole 13 of a part 14a of the main, working, or cutting piston I4, which also comprises the part 14b. A bolt 15 in the sleeve 10 secures the latter to the piston part 14a.

The piston 14 surrounds an ejector piston 16, which is free to move vertically with respect to the former. The ejector piston plays no role in the device of the invention. The table 2 does not rest directly on the main piston I4}, but instead on a cylindrical-sleeve 17, which is rigidly fixed to the table 2 and surrounds the piston part 14a to from with the latter an annular chamber I3 for compressed air. The chamber embodies a threaded connection opening 19 to which is connected a compressed airline 20 having a shutoff valve 21. Once the tool 4 is held on the table 2 and the sheet metal 6 is placed on the tool, sufficient compressed air is let into the chamber 18 through the valve 21 to raise the sleeve I7--and with it the table 2, the tool 4, and the sheet metal ii-from its lowermost position (relative to the piston 14), shown at the right in the FIG, to its upper position, shown at the left, in which the bottom of the recess II presses against the head 12 of the sleeve 10. The pressure in the chamber 18 is only enough to raise the sleeve 17, and thus the table 2, the small distance a above the piston 14. So negligible is the force exerted on the heads 12, which determine this distance a, that the table 2 floats on the compressed air cushion in the chamber 18.

Mounted on the table 2 is a limit switch 22 having an actuator 23 that cooperates with one end of a trip pin 24, which is free to move back and forth in a radial hole 25 of the sleeve 17. The other end of this pin so cooperates with a cam surface ple, only when the sleeve-l7 is in its lowermost position relative to the piston M.

A second limit which 27 is adjustably mounted on the upright 1 so that it can be moved up or down in dependence on the thickness of the metal plate 6. The actuator 28 of this switch so cooperates with the cam surface 29 of a projection 30 on the piston part 14a that the switch is first closed, for example, when the piston 14 is sufficiently raised, relative to the uprights l, to clamp the metal 6 between the cutting tools 4 and 5.

The limit switches 22 and 27 control the drive of the piston I4 through a press control (not shown) that is otherwise conventional. If the main piston 14 is hydraulically driven, for example, the press control incorporates an electrically operated valve that controls the flow of hydraulic oil to and from the cylinder in which the piston strokes.

During the working stroke of the main position 14, the table 2 is moved upwards floating on the compressed air cushion until the metal 6 begins to press against the top tool 5. At this position, the limit switch 27, which is located vertically in dependence on the thickness of the metal 6, is then closed. As the piston 14 continues to rise, the table 2 at first does not continue upwards. It moves downwards relative to the piston 14 against the slight and elastic resistance of the compressed air trapped in the annular chamber 18, causing the limit switch 22 also to close. Only when the sleeve 17 is once again in its lowermost position relative to the piston 14 is the metal blanked or punched as the piston 14 continues to rise. The fact that switch 22 closes after switch 27 is a certain indication that noforeign object 7 is on the metal plate 6, and the control for the main piston 14 is so designed that the press continues to operate automatically with this sequence of switch closings.

If some object 7 is present, it prematurely stops the floating table 2, causing it to move downwards relative to the piston 14 and to close the switch 22 before the switch 27 is closed. The consequence is that .the press is immediately stopped. The press is also stopped, of course, if excessively thick metal is in advertently placed on the tool 4. i

It is perfectly apparent that the described tool safety device of the invention is useful not only with hydraulic stamping presses, but also with other kinds of presses, such as those with an electromechanical drive for swaging forging, coining, and other stamping operations, in which case the blank to be worked or formed can take a form other than that of sheet metal. The safety device of the invention is always called into action when the blank is too high or made too high by a foreign object. The air cushion can be replaced by adjustable springs for floating the table. In principle, the spring arrangement can also be used with .the upper table, the lower table being stationary. Additional pistons can also be provided. With precision stamping presses there can be incorporated a piston for pressing a toothed ring against the sheet metal to hold the latter rigidly taut in a known manner before it is punched or blanked.

Several gaskets 31 and 32 are provided. The piston parts 14a and 14b are held together by bolts, not shown.

In certain cases it may be more advantageous for reasons of construction to arrange the means for mounting the moved tool not movable with respect to the main piston but with respect to some part rigid with the press frame uprights, such as a table rigid with the uprights and located below a vertically stroking main-piston. The said means will then be held, during the working stroke of the press, by the elastically yielding arrangement, such as the compressed air in a chamber, as in the illustrated embodiment, slightly spaced from the part rigidly connected to the uprights: where this part is the table, somewhat above that position in which the said means rests on the table. The fundamental arrangement and functions of the two limit switches are not changed. The second limit switch is still actuated by the projection (27 and 30 in the illustrated embodiment) when the said means is pressed backwards through this small spacing against the elastic resistance of the arrangement and against the said part when the second tool (now the movable one) presses against the blank or against a foreign body on the blank.

Although the preferred embodiment of the invention have been described, the scope of, and the breadth of protection afforded to, the invention are limited solely by the appended claims.

We claim:

1. A tool protection means in a press of the type including a first toolholder stationarily mounted, and a second toolholder facing said first toolholder and mounted for rectilinear reciprocatory movement toward and away from said first toolholder by means of a piston, said tool protection means comprising guide means secured to said second toolholder and contacting said piston in axially slidable engagement therewith, means securing said second toolholder to said piston and adapted to limit the sliding movement of said second toolholder on said piston in a direction away from said piston to establish a maximum separation gap between said second toolholder and said piston, means interposed between said piston and said guide means and adapted to yieldingly urge said second toolholder toward said maximum separation gap position, a first limit switch stationarily and adjustably mounted adjacent to said piston, first switch actuator means secured to said piston for operative cooperation with said first limit switch, a second limit switch secured to said second toolholder adjacent to said sleeve, second switch actuator means for operative cooperation with said second limit switch, said second switch actuator means including a member slidably mounted in a transverse passage through said guide means, and means on said piston for operative cooperation with said member, the adjusted position of said first limit switch being so selected in relation to the thickness of a workpiece interposed between said tools as to cause said first switch actuator means to operate said first limit switch when the tools engage the workpiece, continued movement of the piston in the same direction to close said maximum separation gap against the action of said yielding means causing said second switch actuating means to operate said second limit switch, whereby if said tools are prevented by some foreign object on the workpiece toengage said workpiece said second limit switch is operated prior to said first limit switch thereby causing the movement of the piston to be immediately discontinued.

2. A tool protection means as set forth in claim 1, in which said yielding means include an annular compressed air chamber formed by said piston and guide means, a compressed air supply line connected with said compressed air chamber, and a control valve in said line.

3. A tool protection means as set forth in claim 1, in which said means for operative cooperation with said member comprises a cam surface on said piston. 

1. A tool protection means in a press of the type including a first toolholder stationarily mounted, and a second toolholder facing said first toolholder and mounted for rectilinear reciprocatory movement toward and away from said first toolholder by means of a piston, said tool protection means comprising guide means secured to said second toolholder and contacting said piston in axially slidable engagement therewith, means securing said second toolholder to said piston and adapted to limit the sliding movement of said second toolholder on said piston in a direction away from said piston to establish a maximum separation gap between said second toolholder and said piston, means interposed between said piston and said guide means and adapted to yieldingly urge said second toolholder toward said maximum separation gap position, a first limit switch stationarily and adjustably mounted adjacent to said piston, first switch actuator means secured to said piston for operative cooperation with said first limit switch, a second limit switch secured to said second toolholder adjacent to said sleeve, second switch actuator means for operative cooperation with said second limit switch, said second switch actuator means including a member slidably mounted in a transverse passage through said guide means, and means on said piston for operative cooperation with said member, the adjusted position of said first limit switch being so selected in relation to the thickness of a workpiece interposed between said tools as to cause said first switch actuator means to operate said first limit switch when the tools engage the workpiece, continued movement of the piston in the same direction to close said maximum separation gap against the action of said yielding means causing said second switCh actuating means to operate said second limit switch, whereby if said tools are prevented by some foreign object on the workpiece to engage said workpiece said second limit switch is operated prior to said first limit switch thereby causing the movement of the piston to be immediately discontinued.
 2. A tool protection means as set forth in claim 1, in which said yielding means include an annular compressed air chamber formed by said piston and guide means, a compressed air supply line connected with said compressed air chamber, and a control valve in said line.
 3. A tool protection means as set forth in claim 1, in which said means for operative cooperation with said member comprises a cam surface on said piston. 